Previously, colored ink was produced by adding pigments which reflected or absorbed colors, and process colors were produced by mixing the various pigmented inks on the print medium. These pigments are usually cyan, magenta, yellow, and black (CMYK color model). Use of these colors provides a relatively small color gamut, and is not sufficient to reproduce all colors. To expand the reproducible color gamut, additional colored inks are used, such as Pantone's six-color (CMYKOG) Hexachrome process, adding to the printer's cost and complexity.
The concept of structural color has been addressed in the formation of synthetic opals. In that process, certain sub-micron (250-350 nm) polystyrene spheres and nano-particles of less than about 50 nm in diameter are mixed into a viscous melted carrier fluid that hardens into a flexible sheet as it cools. However, structural color has not previously been addressed in the environment of producing ink using structural color, particularly in real time in a printer.
This innovation expands the range of hues reproducible by printers beyond those obtained with conventional inks. Further, this innovation reduces the complexity of color printers by eliminating the need for spot-color inks or six-color processes to expand the printer's reproducible gamut of colors.